Rail vehicles are usually equipped with wheelsets, by means of which a constant contact between vehicle and rail track and thus a safe support and guidance of the respective rail vehicle is ensured. As a result of this rolling contact, the wheelsets are exposed to direct stresses and are safety-relevant for a controlled vehicle movement. Through its interaction with the rail, the geometry of the wheel running surface determines the running of the vehicles. The wheelset is therefore of particular importance in the maintenance of rail vehicles. The high demands on reliability and quality require regular inspection and assessment of the current component state and the available abrasive wear material.
During vehicle movement operation, the wheel-rail system is subjected to different wear mechanisms due to the constant sliding and rolling movements. In addition to the acoustic disturbance for passengers and the surrounding area, the resulting deformation in the wheel running surface profile also poses the danger of material failure for the wheelset and surrounding components, such as the wheel bearing and undercarriage. This problem is to be counteracted and largely avoided by the so-called reprofiling of the wheel running surface profile.
The aim in designing the wheel running surface profile is a safe, low-wear guide ensuring a comfortable ride. For this reason, contours are realized which take into account the natural wear between wheel and rail. In an ideal case, the contours are either not to change at all, or only slightly, during operation of the rail vehicles.
The resulting wear by the removal of material on wheel and rail depends primarily on the friction in the contact zone and the combination of materials. Here, a basic distinction is made between running surface and wheel flange wear. By combining these two wear profiles, a possible wear profile results which is to be reprofiled.
Such a reprofiling can be carried out with machines for wheelset machining, which are known in various type variants, for example as underfloor or surface versions as well as in flatbed and portal designs. By means of machines for wheelset machining, machining processes are used for machining the wheel running surfaces, preferably by turning, so that these machines are also designated as wheelset lathes.
Starting from the understanding that, as a result of introducing residual compressive stresses into the surfaces of rotation-symmetric objects, wear behaviour can be improved, it has already been proposed to subject selected wheelset sections to an additional deep rolling process directly after wheel manufacture in new condition or at a later date following successful reprofiling. In this way an increase in the further service life of the wheel running surfaces can be achieved by deep rolling.
The deep rolling of the surface is a minimally invasive mechanical re-shaping of the edge layer of the component. During this process, suitable rolling elements are guided over the finished component surface under contact pressure. The direct component contact area is plastically deformed while the adjacent contact area is elastically deformed. Depending on the respective actual contact conditions, only the surface is being finished, with minor notches being levelled or the material in the plastically deformed volume is strengthened.
Thus, when deep rolling is used for wheelsets, the work hardening of the wheel running surfaces achieves a finishing or reduction of the surface roughness, a hardening of the boundary layer and an introduction of residual compressive stresses into the boundary area. Any damaging residual stresses present in the edge layer of the workpiece as a result of the pre-machining cutting are eliminated through the re-shaping. By means of the interaction of elastic and plastic deformations a residual stress state advantageous in terms of strength is newly imprinted. Following deep rolling, residual compressive stresses are present in the external boundary layer; these cause a reduction in the wear of the wheel running surfaces or an increase in the mileage of the rail vehicle wheels. This causes the occurrence of any cracks as well as their progression to be significantly restricted. This exclusively mechanical surface treatment by deep rolling is a very effective, environmentally friendly and resource-saving process.
DE 808 197 describes a roller for the deep rolling of axle journals in railway wheelsets. The working surface of this work roller consists of a cylindrical base body. During deep rolling the axis of the work roller runs at an incline to the axis of the axle journal and generates a strung out drop-shaped impression on the surface to be machined. Accordingly, in the area of the impression, deep rolling introduces residual stresses into the surface of the axle journals, by means of which the occurrence of new cracks is to be avoided and/or the further progression of any existing cracks is to be stopped. Deep rolling results therefore in an increase of the service life of a wheelset.
An additional approach for the deep rolling of cylindrical shafts is known from DE 843 822. This device features one or several work rollers. Here, each work roller is supported in a swivelling carrier the swivel axis of which runs vertically to the feed motion of the work roller and approximately vertically to the wheelset shaft.
Using the device for the deep rolling of wear surfaces on the profile of rough-turned wheelsets according to DE 1 278 274, different relative positions can be set between the work roller, its feed device and the wheelset turning axis.
Although from the references mentioned above, as well as additional references on the state of the art, various variants of wheelset shaft sections selected for deep rolling are known, there continues to be a need for further development. This results in particular from the aspect that wheel running surfaces are rolled by the forward feed process which, with regard to component geometry and the feed component, yields very specific requirements for work rollers that cannot be met, or only met to a limited extent, by the embodiments known so far.